The meter used, Troxler 3216, is a portable instrument with a periodic counter to measure the rate of thermalization of the neutrons.
Since other hydrogen bearing materials also thermalize neutrons, a measurement survey is necessary to establish a relative base level before an analysis can be performed. A measured roof drawing is rendered and a 5’ by 5’ or 10’ by 10’ grid pattern is established on the roof.
A number of readings are then performed to establish a relative base level before the actual analysis is performed. Testing intervals are typically 7.5 seconds at each grid point location.